May 13, 2004
Donald Savage
Headquarters, Washington
(Phone: 202/358-1547)
Cheryl Dybas
National Science Foundation, Arlington, Va.
(Phone: 703/292-7734)
Gail Gallessich
University of California, Santa Barbara
(Phone: 805/893-7220)
RELEASE: 04-159
EVIDENCE OF METEOR IMPACT FOUND OFF AUSTRALIAN COAST
An impact crater believed to be associated with the "Great Dying," the
largest extinction event in the history of life on Earth, appears to
be buried off the coast of Australia.
NASA and the National Science Foundation (NSF) funded the major
research project headed by Luann Becker, a scientist at the
University of California, Santa Barbara (UCSB). Science Express, the
electronic publication of the journal Science, published a paper
describing the crater today.
Most scientists agree a meteor impact, called Chicxulub, in Mexico's
Yucatan Peninsula, accompanied the extinction of the dinosaurs 65
million years ago. But until now, the time of the Great Dying 250
million years ago, when 90 percent of marine and 80 percent of land
life perished, lacked evidence and a location for a similar impact
event.
Becker and her team found extensive evidence of a 125-mile-wide
crater, called Bedout, off the northwestern coast of Australia. They
found clues matched up with the Great Dying, the period known as the
end-Permian. This was the time period when the Earth was configured
as one primary land mass called Pangea and a super ocean called
Panthalassa.
During recent research in Antarctica, Becker and her team found
meteoric fragments in a thin claystone "breccia" layer, pointing to
an end-Permian event. The breccia contains the impact debris that
resettled in a layer of sediment at end-Permian time.
They also found "shocked quartz" in this area and in Australia. "Few
Earthly circumstances have the power to disfigure quartz, even high
temperatures and pressures deep inside the Earth's crust," Becker
said.
Quartz can be fractured by extreme volcanic activity, but only in one
direction. Shocked quartz is fractured in several directions and is
therefore believed to be a good tracer for the impact of a meteor.
Becker discovered oil companies in the early 70's and 80's had drilled
two cores into the Bedout structure in search of hydrocarbons. The
cores sat untouched for decades. Becker and co-author Robert Poreda
went to Australia to examine the cores held by the Geological Survey
for Australia in Canberra. "The moment we saw the cores, we thought
it looked like an impact breccia," Becker said. Becker's team found
evidence of a melt layer formed by an impact in the cores.
In the paper, Becker documented how the Chicxulub cores were very
similar to the Bedout cores. When the Australian cores were drilled,
scientists did not know exactly what to look for in terms of evidence
of impact craters.
Co-author Mark Harrison, from the Australian National University in
Canberra, determined a date on material obtained from one of the
cores, which indicated an age close to the end-Permian era. While in
Australia on a field trip and workshop about Bedout, funded by the
NSF, co-author Kevin Pope found large shocked quartz grains in
end-Permian sediments, which he thinks formed as a result of the
Bedout impact. Seismic and gravity data on Bedout are also consistent
with an impact crater.
The Bedout impact crater is also associated in time with extreme
volcanism and the break-up of Pangea. "We think that mass extinctions
may be defined by catastrophes like impact and volcanism occurring
synchronously in time," Becker said. "This is what happened 65
million years ago at Chicxulub but was largely dismissed by
scientists as merely a coincidence. With the discovery of Bedout, I
don't think we can call such catastrophes occurring together a
coincidence anymore," she added.
For information and images about the research on the Internet, visit:
http://beckeraustralia.crustal.ucsb.edu/
For information about NASA's Astrobiology research on the Internet,
visit:
http://astrobiology.arc.nasa.gov/
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